You could have your students post their writings here, and other students could post discussions about their writings. An example of a school who has done this can be viewed at
http://brickwall.wikispaces.com
On this space, you would choose a student from the left list and look at their work. Keep in mind, I think that this teacher has let them make their own home page, and then you would choose a writing from the list you find on the the left. Some of these students have posted discussions to the writings. You can see these by clicking on the discussion tab at the top of the page.

Another idea could be to do literary circles. An example of one can be found here: http://litcirclesrau.wikispaces.com. This is a wikipage that few students here are working on currently. This link will take you to my home page, find litcirclesrau on the left.

You could also post discussion boards on controversial topics. See the link below.
6 Great Things About Schools

You could have a list of articles for the students to read, require them to read and discuss a certain number of these articles, and then respond to a certain number of student's responses. Now you have classroom collaboration, or collaboration even between students in different periods.

You could allow students to create a report using a wikipage, with links to pictures, research, writings, etc. This could include a lesson on copyrighting. The possibilities are endless! See me for help setting up a free wikipage, or go to http://wikipages.com/site/for/teachers.